A color diffusion transfer photography has heretofore been known comprising a dye-forming compound which provides a dye having a different diffusivity from that of the dye-forming compound itself as a result of the development of silver halide under an alkaline basic condition. In such a system, three color dyes, i.e., yellow, magenta and cyan dyes are normally used to form color images which have little or no absorption in a wavelength region longer than visible light region, i.e., infrared region. In general, the edge of absorption by a cyan dye in a long wavelength region extends to 700 nm or longer. However, no cyan dyes are known which have a strong absorption in the infrared region.
In recent years, on the other hand, optical character readers and label bar code readers have been developed and put into frequent use. Thus, these readers have acquired greater importance. Most of these readers are equipped with a light-emitting diode or semiconductor laser which emit light having a wavelength of 700 nm or longer as a light source for reading.
In another apparatus which is widely used, a tungsten lamp is used as a light source and an element having a peak of light-receiving sensitivity in the vicinity of 900 nm and a sensitivity region in the range of about 700 to 1,200 nm is used as a light-receiving element. However, since images formed from the above described dyes have little or no light absorption in the near infrared region of 700 nm or higher, these image data cannot be read or can be hardly read by these readers.
Thus, it has been keenly desired to provide a diffusion transfer type color image-forming compound having light absorption in a wavelength region of 700 nm or higher, preferably 750 nm or higher.